Highly Selective and Durable Photochemical CO₂ Reduction by Molecular Mn(I) Catalyst Fixed on a Particular Dye-Sensitized TiO₂ Platform

Abstract

A Mn­(I)-based hybrid system (OrgD-|TiO2|-MnP) for photocatalytic CO2 reduction is designed to be a coassembly of Mn­(4,4′-Y2-bpy)­(CO)3Br (MnP; Y = CH2PO­(OH)2) and (E)-3-[5-(4-(diphenylamino)­phenyl)-2,2′-bithiophen-2′-yl]-2-cyanoacrylic acid (OrgD) on TiO2 semiconductor particles. The OrgD-|TiO2|-MnP hybrid reveals persistent photocatalytic behavior, giving high turnover numbers and good product selectivity (HCOO– versus CO). As a typical run, visible-light irradiation of the hybrid catalyst in the presence of 0.1 M electron donor (ED) and 0.001 M LiClO4 persistently produced HCOO– with a >99% selectivity accompanied by a trace amount of CO; the turnover number (TONformate) reached ∼250 after 23 h of irradiation. The product selectivity (HCOO–/CO) was found to be controlled by changing the loading amount of MnP on the TiO2 surface. In situ FTIR analysis of the hybrid during photocatalysis revealed that, at low Mn concentration, the Mn–H monomeric mechanism associated with HCOO– formation is dominant, whereas at high Mn concentration, CO is formed via a Mn–Mn dimer mechanism.

Organometallic Iridium(III) Complex Sensitized Ternary Hybrid Photocatalyst for CO2 to CO Conversion

“…The performance rise stops with a further increase of the IrP loading amount (>1.25 μmol); thus we found the optimum loading conditions of IrP to be 1.0 μmol on 10 mg TiO 2 /ReP (Table ). This is consistent with the dye concentration dependency observed in our previous Re I ‐based ternary analogues (dye/TiO 2 /Re I catalyst) . Figure shows typical plots of TON and μmol versus irradiation time for the CO formation of the IrP (0.1 μmol)/TiO 2 /ReP ternary series.…”

“…[14] The dye-sensitized photocatalysis (DSP) approachi nvolves an n-type TiO 2 semiconductor as an electron mediator anda sa scaffold that ideally links the molecular or metal components by coadsorption onto the TiO 2 surface. [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] The DSP system rapidly consumes the reactive excited (IrPS*) or reduced (IrPSC À )s pecies with the alleviation of intermoleculari nteraction by low average coverage of the PS, consequently lessening the photodegradation of IrPS. Such coassembly of components onto as emiconductor surfacec an also allow no limitation of solvent selection based on heterogenization, with easy preparation and tunability of the DSP system.…”

“…The dye‐sensitized photocatalysis (DSP) approach involves an n‐type TiO 2 semiconductor as an electron mediator and as a scaffold that ideally links the molecular or metal components by coadsorption onto the TiO 2 surface . The DSP system rapidly consumes the reactive excited (IrPS*) or reduced (IrPS .− ) species with the alleviation of intermolecular interaction by low average coverage of the PS, consequently lessening the photodegradation of IrPS.…”

Electro‐ and Photochemical Reduction of CO2 by Molecular Manganese Catalysts: Exploring the Positional Effect of Second‐Sphere Hydrogen‐Bond Donors

“…This behavior is consistent with the concentration‐dependent product selectivities reported here. A similar observation was reported by Kang and co‐workers with a phosphonate‐functionalized Mn(bpy)(CO) 3 Br system attached to a dye‐sensitized TiO 2 platform for photocatalytic CO 2 reduction, which exhibited a surface‐loading dependence favoring formate production at low catalyst loadings [33] . These results demonstrate that site isolation (or very low catalyst concentrations in the present homogeneous study) of molecular MnBpy‐type catalysts can determine product selectivity, where HCO 2 H (or HCO 2 − ) production is favored via a mononuclear catalytic cycle.…”

Dye‐Sensitized Heterogeneous Photocatalysts for Green Redox Reactions

“…Using dye DH (Figure ) and BIH as SED, different reduction catalysts have been tested in order to prepare products other than CO. Anchoring both catalysts ReP (Figure ) and CoP 1 (Figure a), Kang et al were able to produce both CO and H 2 (syngas), and the ratio between the two gases was adjustable by varying either the amount of water in the solvent mixture (0–20 %) or the molar ratio of the two catalysts . By contrast, anchoring of MnP catalyst (Figure ) allowed to obtain formate as the main product with a TON formate of ≈ 250 after 23 h of irradiation (> 400 nm, 60 W) . Selectivity of the system towards the formate production was a matter of Mn concentration on the TiO 2 surface, since loading of the catalyst higher than 0.1 µmol favored the formation of Mn‐Mn dimers, which are more selective towards the formation of carbon monoxide instead of formate.…”